Sender ID is what appears on people's phones to show who the SMS is from. With Nexmo this is usually defined by the &from= parameter in your API request.

When someone sends you an SMS, the Sender ID is set to that person’s phone number. But over an API, this alpha-numeric variable can be set to any 15 digits or 11 characters in the range a-z, A-Z plus 0-9. Brands love this because it enables them to set their brand name as the SenderID.

There are local restrictions and in some markets, such as North America or Brazil, the Sender ID cannot be changed. In some other destinations only certain senders are allowed (i.e. only alpha senders, or international numerics) so senders not complying with local regulations may be overwritten, either by the operator or by Nexmo, to ensure the message is delivered.

What variations of Sender ID are there?

Fully Dynamic - You can define your Sender ID as you wish, with the only restrictions being length and needing to use characters from the range 1234567890abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ

Characters outside this range (e.g. <space>) may or may not be supported depending on the destination operator.

Dynamic alpha - You can set any SenderID you like up from a minimum of 4 to maximum 11 characters as long as it only uses letters. Keep in mind that Alpha SIDs can only be used for one-way messages. Since the Alpha SID is not a phone number, it cannot receive replies.

Dynamic numeric - You can set any SenderID you like up to 15 digits as long as it only uses numbers

Random Numeric - Nexmo will apply a random number to comply with local regulations (usually taken from a pool of numbers we have access to from the relevant destination market)

Fixed SenderID - This is where the local markets require Nexmo to set a fixed SenderID, sometimes numeric, sometimes alpha, in order that messages are permitted to be delivered